1. Field of the Invention
The present invention relates generally to the field of vacuum package testers, and more particularly to improved apparatus capable of providing data by which the internal pressure and volume of residual gas of a flexible wall vacuum package, exposed to a known external pressure, may be calculated.
2. Description of the Prior Art
Flexible wall vacuum packages are widely known, and are commonly used to package perishible food products such as meat. Bacon, sausage, hot dogs and the like are often contained in such packages.
The shelf life of the food product is inversely related to the amount of residual oxygen within the package, which can promote bacteria growth. Vacuum packages, in which the flexible package wall assumes the general contour of the packaged product, were developed largely in an attempt to reduce the amount of oxygen in the package, and thereby increase the shelf life of the product. With this known technique, the product is packaged in a relative vacuum. The package may be also subjected to a shrink fit technique. The end result is that the pressure within the package is sub-atmospheric, and the pressure differential across the packaged wall causes the wall to assume the contour of the packaged article.
However, after the product has been packaged, it would be highly desirable to determine: (1) the pressure within the package; (2) the percentage of total package volume which is occupied by gas; (3) the volumetric percentage of residual oxygen within the package; and (4) the actual volume occupied by residual gas. Tested samples could indicate defects in manufacturing processes, and serve as an indicator of the product's estimated shelf life.
Prior art publications concerning such vacuum packages, sometimes called "retort pouches", and testing methods therefor, include: Rizvi, "Retortable Pouches: Food Package of the Future?", Agri-Search, S.C. Agricultural Research Station, Clemson University (Summer 1980); Lampi, "Flexible Packages for Thermoprocessed Foods", Advances in Food Research, Academic Press, New York (Vol. 23, 1977); Technical Report 73-4-GP, Shappee and Werkowski, "Study of a Nondestructive Test for Determining The Volume of Air in Flexible Food Packages", U.S. Army, Natick Laboratories, Natick, Mass. 01760 (June 1972); and Ghosh and Rizvi "Nondestructive Determination of Residual Volume of Air in Retort Pouches", South Carolina Agricultural Experiment Station, Clemson University.